WO2009012807A1

WO2009012807A1 - Setting up a call in a telecommunications network by addressing the destination with an uri in a circuit switched call setup request message

Info

Publication number: WO2009012807A1
Application number: PCT/EP2007/057538
Authority: WO
Inventors: Rogier Noldus; Erwin Van Rijssen
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2007-07-20
Filing date: 2007-07-20
Publication date: 2009-01-29

Abstract

A method, apparatus and computer program for setting up a call in a telecommunications network, between a user equipment operating in circuit switched mode and a destination, the method comprising the step of sending a circuit switched (CS) call set up request to a call routing server, wherein the user equipment receives a URI as a destination identifier and sends a CS call set up request carrying said URI to a call routing server. The call routing server forwards the call set up request to a translation means, which, if necessary, translates the URI to a corresponding telephone of the destination. The call routing server routes CS call set up request towards the destination.

Description

SETTING UP A CALL IN A TELECOMMUNICATIONS NETWORK BY ADDRESSING THE DESTINATION WITH AN URI IN A CIRCUIT SWITCHED CALL SETUP REQUEST MESSAGE

TECHNICAL FIELD The invention relates to telecommunication systems and, more particularly, to a method, system and devices for requesting a call set up in a telecommunications network from a user equipment operating in circuit switched mode to a destination by using a Uniform Resource Identifier, URI.

BACKGROUND

In present day telecommunications networks, Internet Protocol, IP, based networks such as IP Multimedia Subsystem, IMS, networks, coexist next to circuit switched, CS, mobile networks such as the Global System for Mobile Communications, GSM, and the Universal Mobile Telecommunications System, UMTS. The way in which a session, that can be a call, a packet data communication or in general any communication, between a calling party and a called party is established, differs between CS GSM or CS UMTS on the one hand and IMS on the other hand.

A call from a user of a GSM terminal, referred to for example as user equipment UE, starts when a mobile subscriber first keys in the desired called party number or service code and then presses the send or call key. An access channel is seized, whereupon the entered number is automatically transmitted to a Mobile Switching Centre, MSC, via a Base Transceiver Station and Base Station Controller. The keyed number is analyzed by the MSC in order to determine whether the caller is allowed to call that particular number or to invoke a subscriber feature associated with the entered service code or associated with the calling party. If this and other analyses in the network are affirmative, then the mobile station is assigned to a digital voice channel and the call is set up.

In IMS networks the session between two parties is set up in a different way, using the Session Initiation Protocol, SIP. The IMS supports, amongst others, voice calls, data calls and video calls. SIP is a signaling protocol used to create, manage and terminate sessions in an IMS network and in a non-IMS network. A session may be a simple two- way telephone call or a multi-media conference session. This makes it possible to implement services like voice-enriched e-commerce, web page click-to-dial or Instant Messaging with buddy lists in an IP based environment.

Details on the Session Initiation Protocol can be found in the standard RFC 3261 as put forward by the Internet Engineering Task Force, IETF. The primary task of SIP is the set up of sessions. The details of the data exchange within a session e.g. the encoding or codec issue related to audio/video media is taken care of by other protocols.

A Uniform Resource Identifier, URI, is an addressing type for identifying resources on the Internet or private intranet. URIs were originally defined as two types: Uniform Resource Locators, URLs, which are addresses comprising network locations, and Uniform Resource Names, URNs, which are persistent names that are independent from the underlying address.

The terms URI and URL are used synonymously, but URL is more widely used in everyday conversation. In technical documentation from the standards committees, however URI is the preferred term. In the present invention the term URI is therefore used to refer to any resource indication on the internet or private networks.

A SIP URI is a URI used by the IMS network for identification of subscribers of the IMS network. The SIP URI is communicated to friends and other calling or called parties next to or instead of their regular, numerical telephone number according to the ITU standard E.164. The E.164 standard comprises a format for international telephone numbers and uses a country code, area code and subscriber number. The E.164 number is used to identify a destination in a telecommunications network.

A destination can comprise a destination party, such as another user equipment, a service provider (server/proxy), or another network. The destination can also comprise a service, such as televoting or voicemail. The mentioned examples for destinations can be used in any combinations with each other as well.

A destination may be associated to a circuit- or a packet switched part of the network, or to a combination of circuit- and packet switched part of the network. There are multiple formats available for identifying subscribers in various networks; for example John Smith may communicate to his friends that he may be called by his SIP URI john.smith@abc.com and/or his E.164 mobile telephone number +31652123456.

To set up a SIP call addressed to a certain SIP URI, currently a SIP enabled user equipment is required. If a user would like to use one and the same user equipment for both GSM calls and SIP calls, that user currently needs a dual mode user equipment which is able to provide GSM user equipment possibilities as well as access to the Internet to set up a SIP call.

WO 03/010945 discloses a system and method for establishing a call in a telecommunications network such as Public Switched Telephone Networks, Public Land Mobile Networks, Asynchronous Transfer Mode networks, Internet Protocol Multimedia Subsystems or third generation mobile networks. For call establishment a URL is translated into a corresponding E.164 telephone number.

SUMMARY

It is an object of the present invention to provide a method and a device for setting up a telephone call addressed towards a URI independent of the operation mode of a user equipment.

This problem is solved by the teaching of the independent claims. Further preferred embodiments are described in the dependent claims.

The invention provides a method for setting up a call in a telecommunications network, between a user equipment operating in circuit switched mode and a destination, the method comprising the step of sending a circuit switched call set up request from the user equipment to a call routing server, wherein the user equipment receives a Uniform Resource Identifier, URI, as a destination identifier of the call to be set up, and wherein the circuit switched call set up request comprises the URI as the destination identifier of the destination to where the call is to be set up to. This has the advantage that a user can use a regular GSM telephone that is modified according the invention to send a URI, instead of use a special IMS phone. An additional advantage is that the user does not need to subscribe to IMS services for this use case.

The invention provides furthermore a method for setting up a call in a telecommunications network, between a user equipment operating in circuit switched mode and a destination. The method comprises the steps of receiving at a call routing server a first circuit switched call set up request comprising a Uniform Resource Identifier, URI, as a destination identifier of a call to be set up, generating by the call routing server responsive to the circuit switched call set up request a second call set up request, said second call set up request comprising the URI, sending by the call routing server the second call set up request to a translation means, determining by the translation means a telephone number corresponding to the URI of the destination, sending the determined number to the call routing server, and proceeding by the call routing server with the call set up based on the telephone number.

This method has the advantage that the translation can be done by a central node having access to a database with corresponding E.164 numbers. The user of the user equipment does not need to maintain such a database, which reduces effort and memory resources on the user equipment.

According to a further embodiment the translation means translates the URI, such as a SIP URI, of the second call set up request to a corresponding telephone number of the destination. The URI may be represented by address digits of a Binary Coded Decimal (BCD) number used to identify the destination. This has the advantage that the standard use of the BCD number will not be affected, and at the same time this will enable the user equipment to send the URI to the routing server in an easy manner.

The invention further proposes a user equipment operating in circuit switched mode, adapted to request a call set up to a destination in a telecommunications network. The user equipment comprises an input interface comprising means for receiving a URI identifying a destination, a processor unit comprising means for composing a circuit switched call set up request including said URI, and an output interface comprising means for sending said circuit switched call set up request to a call routing server.

This has the advantage that the user equipment does not have to be capable to operate in a packet switched mode.

In one embodiment the user equipment provides an interface to receive as an input from the user the entered URI. Alternatively or in addition, the interface of the user equipment comprises means for receiving the URI included in a message from a destination such as the called party or any network node. The message can comprise e.g. a Short Message Service, SMS, message or a Multimedia Messaging Service, MMS message.

The user equipment provides in a preferred embodiment a memory for storing the URI in an address book of the user equipment. The memory is connected to the processor unit.

Further aspects of the invention refer to the user equipment being adapted for manual selection of the URI by the user, and / or to select the URI automatically from the message, and / or for a selection of the URI from the address book.

The invention further proposes a call routing server in a telecommunications network, which comprises an input interface for receiving a first circuit switched call set up request, the circuit switched call set up request requesting a call set up to a destination, a processor unit connected to the input interface for generating responsive to the first circuit switched call set up request, a second circuit switched call set up request, and an output interface connected to the processor unit for sending the second call set up request towards the destination. The processor unit comprises means for generating the second circuit switched call set up request by processing a URI identifying the destination, said URI being comprised in the first call set up request.

In one embodiment the call routing server, e.g. an MSC, comprises means for sending a request for a destination identifier, comprising the URI, to a translation means. The call routing server is optionally comprising means for determining if the second call set up request is to be sent towards the destination in a circuit switched mode or in a packet switched mode.

The invention further proposes a translation means in a telecommunications network comprising an input interface for receiving from a call routing server a request for a destination identifier. The request comprises a URI. A processor unit is connected to the input interface for translating the URI into the destination identifier (e.g. a corresponding E.164 telephone number), and an output interface is connected to the processor unit for sending the destination identifier to the call routing server.

According to one embodiment, the translation means comprises means for sending the URI as destination identifier for identifying the destination in a packet switched part of the network. The translation means is preferably comprised in the call routing server or co-located with the call routing server, or it comprises a Service Control Point. According to a further embodiment the translation means comprises means for processing a BCD number comprised in the circuit switched call set up request. The BCD number comprises the URI.

The invention further proposes a computer program product loadable into the internal memory of a digital computer, comprising software code portions for performing the steps of the method as proposed by the invention when said product is run on a computer.

This supports an easy way of operation, maintenance and upgrading in a network node.

In one embodiment the computer program product is stored on a computer usable medium.

The invention further proposes a circuit switched call set up request message, characterized in that the circuit switched call set up request message comprises a URI as a destination identifier, identifying a destination of a call set up requested by the circuit switched call set up request message.

A further embodiment refers to the circuit switched call set up request message that comprises only a URI as destination identifier identifying the destination of the call set up requested by the circuit switched call set up request message. In this case the call set up message does not comprise a Circuit Switched destination identifier at all, in which case the invention is in particular advantageous for users who own a single GSM mode terminal only.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail with reference to the following figures.

Figure 1 shows a message sequence diagram illustrating a call set up request according to an embodiment of the invention. Figure 2 shows a message sequence diagram illustrating a call set up according to a further embodiment of the invention.

Figure 3 shows a diagram illustrating an embodiment of the invention of the sending of a

SIP URI from a CS user equipment towards a circuit switched network.

Figure 4 shows a diagram illustrating a further embodiment of the invention of the sending of a SIP URI from a CS user equipment to a destination in the IMS network.

Figure 5 shows a diagram illustrating an embodiment of an MSC according to the invention.

Figure 6 shows a diagram illustrating a further embodiment wherein the MSC routes the call directly to an IMS network. Figure 7 shows a simplified block diagram of a user equipment.

Figure 8 shows a simplified block diagram of a Call Routing Server, such as an MSC.

Figure 9 shows a simplified block diagram of a Translation Means, such as an SCP.

Figure 10 shows an embodiment of a call set up request message. DETAILED DESCRIPTION

In the following the invention is described with respect to a GSM system. It shall be noted however, that the invention can be applied to any circuit switched system or any system that conventionally does not make such use of URI as addressing scheme.

When setting up a GSM call, the GSM user equipment sends a Direct Transfer Application Part, DTAP, Setup message to the Mobile Switching Center, MSC. The DTAP Setup message contains the entire destination number, carried in a Called Party Binary Coded Decimal, BCD, Number. The BCD number refers to numbers in which each decimal digit is represented in binary format and is stored in a single character, byte or semi-octet. For example, if one BCD encoded digit is represented with four bits, then a 12-digit number would take 6 bytes of address space. This is described in for example 3GPP Technical Specification (TS) 24.008 Rel-5 version 5.16.0, section 9.3.23.2. The parameter Called party BCD Number is referred to in section 10.5.4.7 of the specification. This parameter may contain 40 octets for the actual called party number, i.e. excluding the number frame.

The number frame of the Called party BCD Number contains, amongst others, the parameters "Numbering Plan Identification" (NPI)" and "Type of Number" (TON). NPI and TON may e.g. indicate E.164 number in international format. The TON field indicates to the system that receives the call whether the digits provided represent a national number, an international number or other type of number.

The present invention proposes that a SIP URI is included in the Called party BCD Number. Preferably, an appropriate combination of values for TON and NPI, such as NPI: "SIP URI" in combination with TON: "public", is used to indicate that the address digits in Called Party BCD Number contain a SIP URI.

Although such an indication is not necessary, it allows, if available, for an easy identification of the address type.

CAMEL (Customized Applications for Mobile Network Enhanced Logic) is a network feature for the network operator to provide the subscribers with the operator specific services even when roaming in another network. The Called Party BCD Number is reported to a CAMEL Service in the so-called Initial DP, IDP, message according to 3GPP TS 23.078 Rel-5 version 5.11.0, section 4.6.1.8. The CAMEL service may by employing a translation means to translate the reported SIP URI into a corresponding E.164 number, which may then be used for routing the call through the circuit switched network.

In the following, examples are described, wherein the user equipment uses particular values for TON and NPI. For example, when establishing a call to a called party known to the calling party as 'John Smith', the user equipment uses 'Universal resource locator' for NPI and 'private' for TON. As another example, when establishing a call to a called party known to the calling party as 'john.smith@abc.com', the user equipment uses 'Universal resource locator' for NPI and 'public' for TON. The MSC receives the DTAP Setup message and starts a CAMEL service, based on the fact that the subscriber has Originating - CAMEL Subscription Information, O-CSI, in the user's Visited Location Register, VLR profile. According to the CAMEL standard, the Called Party BCD Number is reported to a Service Control Point, SCP, in unmodified form. Hence, the SIP URI is implicitly reported to the SCP. The SCP deduces from NPI and TON that the Called Party BCD Number contains a SIP URI. Deduction can be done by reversing the way in which the SIP URI was constructed in the Called Party BCD number by the user equipment. The SCP detects for example that the Called Party BCD number comprises signs such as "@" or ".com", which indicated the presence of a URI. The string comprising such signs can be identified as URI and accordingly be processed as such.

CAMEL Application Part, CAP, is a real time protocol used to support the information flows between CAMEL functional elements such as the Service Control Function, SCF and Service Switching Function, SSF.

In the giving context, the SCP can perform the following different activities:

(1 ) The SCP translates the SIP URI to an E.164 number and sends a CAP Connect message, containing that E.164 number. The call is routed into the CS network, or (2) The SCP does not modify the number. The MSC uses the SIP URI to route the call to the IMS domain. This is only possible when the MSC supports SIP.

From this point forward, the call establishment continues in a conventional manner. It shall be understood that instead of using CAP, another IN protocol may be used such as CS1 , CSI+ or lNAP.

The invention will now be described with reference to the figures. In the drawings, like or similar elements are designated with identical reference numerals throughout the several views. The depicted lines between the elements represent connections between these elements. The arrows represent connections wherein a direction of a message from one element to another element is shown. The term connection refers to a functional connection and not necessarily to a physical connection.

Figure 1 shows a message sequence diagram of a call setup request illustrating a method of the invention. The user equipment 101 first receives 120 a Uniform Resource Identifier, URI, as a destination identifier and then sends 121 a circuit switched call set up request carrying said URI to a call routing server 102.

Figure 2 shows a message sequence diagram illustrating how the circuit switched call set up request is processed according to the invention. Here, after receiving the circuit switched call setup request carrying the URI, the call routing server 102 forwards 122 the call set up request to a translation means 103. The translation means 103 translates 130 the URI into a corresponding telephone number of the destination. The translated URI is used for the call set up process as described in the description.

Figure 3 shows a diagram illustrating an embodiment for the sending of a SIP URI from a CS user equipment to a destination in a circuit switched part of a network.

A user equipment 101 in the CS domain sends 121 a circuit switched call set up message such as a DTAP Setup message to an MSC 102. The DTAP Setup message contains a SIP URI in the Called Party BCD Number. Based on service subscription data in the MSC 102, the MSC 102 invokes an IN service in an SCP 103 by sending 122 a CAP Initial DP, IDP, message to the SCP 103. The MSC 102 includes the Called Party BCD Number, containing the SIP URI, in the CAP IDP. The SCP 103, containing a translation means, translates the SIP URI into a corresponding E.164 number and sends the E.164 number to the MSC 102 by sending 123 a CAP Connect message to the MSC 102.

An ISUP Initial Address Message, IAM, can be found in SS7, Signaling System No.7, signaling networks as part of the Integrated Services Digital Network User Part, ISUP, call set up. This ISUP IAM is used to seize a circuit and transfer addressing and call handling information and routing information.

The MSC 102 sends 124 such an ISUP IAM into the circuit switched, CS, network. The ISUP IAM contains a Called Party Number, which comprises the E.164 number received from the SCP in the CAP Connect message.

Figure 4 shows a diagram illustrating an embodiment for the sending of a SIP URI from a CS user equipment to a destination in an IMS network. A user equipment 101 in the CS domain sends 121 a DTAP Setup message to an MSC 102. The set up message contains a SIP URI in the Called Party BCD Number. Based on service subscription data in the MSC 102, the MSC 102 invokes an IN service in an SCP 103 by sending 122 CAP IDP message to the SCP 103. The MSC 102 includes the Called Party BCD Number, containing the SIP URI, in the CAP IDP. The SCP 103, having determined that the MSC 102 has a direct connection with the IMS network, sends 223 an instruction, by means of a CAP Continue message, to the MSC 102, to route the call towards the SIP URI received in the DTAP Setup message. The MSC 102 sends 224 a SIP Invite message into the IMS network. The SIP invite message comprises a Request URI message, which comprises the SIP URI received in the DTAP Setup message.

Figure 5 illustrates an MSC, wherein the MSC receives a SIP URI from a user equipment and wherein the destination is a device in a circuit switched part of the network. A user equipment 101 in the CS domain sends 121 a DTAP Setup message to an MSC 102, whereby this DTAP Setup message contains, amongst others, the SIP URI of the called party. The SIP URI is carried in the Called Party BCD Number.

Within the MSC 102, a Call Establishment Module, CEM 301 instructs 321 an Invocation Preparation Module, IPM, 302 to establish the call. The subscriber has a subscription to a CAMEL service, so this information flow 321 comprises an Originating - CAMEL Subscription Information, O-CSI. The CEM 301 is in connection with the Radio Access Network, RAN, (not shown) and performs the call establishment process. The CEM 301 verifies, amongst others, whether the user has a subscription to the requested Basic Service (speech call) and whether the subscriber has a subscription to additional services (e.g. CAMEL Service).

The IPM 302 receives the O-CSI from the VLR (not shown) and hands the call control over to a GSM Service Switching Function, gsmSSF, 303. For this purpose, the IPM 302 instructs 322 the gsmSSF 303 of the MSC 102 to invoke an IN service (CAMEL service). The gsmSSF 303 sends 122 a CAP Initial DP, IDP message to an SCP 103 to invoke the CAMEL service logic. The CAP IDP comprises the SIP URI.

The SCP 103 sends 123 a CAP Connect, CON, message to the gsmSSF to supply the translated number to the MSC 102, e.g. the number +46 8 750 2400. The gsmSSF 303 instructs 323 the Number Analysis & Route Module, NAM 304, which is responsible for analyzing the number received from SCP and for selecting an ISUP route towards the called party. The NAM 304 processes the number received from the SCP 103 and sends 124 an ISUP Initial Address Message, IAM, to establish the call over ISDN into the CS network.

Figure 6 shows a diagram illustrating an embodiment whereby an MSC is configured to route the call directly to an IMS network. The MSC in figure 6 is located in a UMTS network. In this example an MSC 102 has support for SIP signaling. The subscriber has an International Mobile Subscriber Identity, IMSI, that belongs to a specific IMSI series. For this IMSI series, the MSC 102 uses a SIP route to IMS for the corresponding subscriber, based on calling party number analysis and called party number analysis. As a result, the call is routed straight from the MSC to the IMS domain. The SIP URI that is used to set up the call does not need to be converted to an E.164 number; it can be copied unmodified to the outgoing SIP URI. The process is described in detail as follows.

A user equipment 101 in the CS domain sends 121 a DTAP Setup message containing the SIP URI of the destination to a Radio Network Controller, RNC, 104, which forwards 422 the message towards the MSC 102. The DTAP Setup message passes through a Node-B (not shown), between the user equipment 101 and RNC 104. The routing of the call to IMS does not require CAMEL control. Alternatively or in addition to using dedicated IMSI series, the subscriber's user profile in an HLR comprises a designated subscription type indicator. This designated subscription type indicator is sent from the HLR to a MSC/VLR (not shown); the MSC 102 uses this subscription type to route 423 calls established by this subscriber directly to a Proxy Call Session Control Function, P- CSCF, 106. The P-CSCF 106 is the first point of contact within the IMS for the user equipment 101. The P-CSCF 106 may be located in the home or visited network. The MSC 102 is configured to use the address of the P-CSCF 106, being an access node for IMS, for this IMSI series. Due to the SIP breakout to IMS, this call is not subject to B- number analysis etc. in MSC 102. The address of the P-CSCF 106 may be part of the designated subscription type indicator. The P-CSCF 106 forwards 424 the SIP message to a Serving Call Session Control Function, S-CSCF, 107. The S-CSCF is the function that registers the user and provides service to them. It performs routing and translation, provides billing information to mediation systems, maintains session timers etc. A SIP Application Server (SIP-AS) 108 is triggered 425 by the S-CSCF which will redirect certain sessions to the SIP-AS. The SIP-AS itself comprises filter rules to decide which of the possible many applications deployed on the server should be selected for handling the session.

The payload (e.g. voice) is routed 426 from the RNC 104 to a circuit switched Media Gateway, CS-MGW, 105, under instruction 427 from the MSC 102. From the CS-MGW 105, the payload may be routed 428 to the IMS domain. Figure 7 shows a simplified block diagram of a user equipment. The user equipment 101 comprises an Input Interface 1011 for receiving a (SIP) URI as destination identifier. The URI is processed by the Processor Unit 1012. Processing refers in this case to composing a CS call set up request that includes the URI. In order to compose this request, the processor unit adds in one embodiment the URI to the address digits of the Binary Coded Decimal number used to identify the destination. The Output Interface 1013 comprise means for sending the CS call set up request to a call routing server such as an MSC.

The user equipment provides optionally a memory 1014 for storing the URI in an address book of the user equipment. The memory is connected to the processor uni 1012.

A mobile telephone is provided that offers a convenient menu for entering a phone number for establishing a call. E.g. when opening the flap (or clamshell), the phone offers a touch keypad, consisting of 0-9, ^* and #. Such a phone that supports SIP-URI calling has the option, when having activated this call menu, to display an alpha-numeric touch keypad. The user can now enter a SIP URI on the phone and set up a call to that SIP URI. The invention proposes an enhanced menu, or an enhanced alpha-numerical keypad, or in general an enhanced graphical user interface to e.g. display the @ sign, prompting the user to enter the identifier and the domain of the user to be called.

If the user inputs a non-public SIP URI, e.g. John smith, then the user omits the domain field. In such case, the SIP URI has meaning only within a Virtual Private Network, VPN, of a calling party; the VPN service will then translate the non-public SIP URI to a public SIP-URI. By use of non-public SIP URIs, a short code dialing service can be realized in a similar way.

Figure 8 shows a simplified block diagram of a Call Routing Server, such as an MSC. The Call Routing Server 102, comprises an Input Interface 1021 for receiving a first request, in a CS mode, for a call set up to a destination. The first request includes a URI identifying the destination. The Processor Unit 1022 comprises means (not shown) for composing a second call set up request responsive to the first request. The Processor Unit 1022 comprises means (not shown) for processing a BCD number which is included in the request and which comprises address digits containing the URI. The Output Interface 1023 comprises means (not shown) for sending the second request towards the destination.

Figure 9 shows a simplified block diagram of a Translation Means, such as an SCP. The Translation Means 103 comprises an input interface 1031 for receiving from a call routing server a request for a destination identifier. The request message includes a URI. The Processor Unit 1032 is connected to the input interface 1031 and is adapted to translate the URI to the destination identifier. The Output Interface 1033 is connected to the Processor Unit 1032 and is adapted to send the destination identifier to the call routing server. The translation means 103 can translate the URI to a corresponding E.164 telephone number for identifying said destination, but may also decide that the URI does not have to be translated, because the destination is associated to a packet switched part of the network, for which a URI is sufficient to identify the destination.

Preferably, the translation means 103 can process a BCD number included in the circuit switched call set up request. The BCD number represents address digits containing said URI.

Figure 10 shows a simplified circuit switched message 109. The message comprises a Uniform Resource Identifier, URI 1091 as a destination identifier identifying a destination of a call set up requested by the circuit switched call set up request message. Part of the message are fields such as Type Of Number, TON 1092, which is in this example set at a value "public", meaning that the type of number is publicly known. The Numbering Plan Identification, NPI 1093 is set at "SIP URI", indicating a SIP URI. The invention has been illustrated by the accompanying figures and described in the foregoing description. However, it is to be understood that the invention is not limited to the particular embodiments described, but is defined by the following claims.

Claims

1. A method for setting up a call in a telecommunications network, between a user equipment operating in circuit switched mode and a destination, the method comprising the step of sending a circuit switched call set up request from the user equipment to a call routing server (102), characterized in that: the user equipment (101 ) receives (120) a Uniform Resource Identifier, URI, as a destination identifier of the call to be set up, - wherein the circuit switched call set up request comprises the URI as the destination identifier of the destination to where the call is to be set up to.

2. A method for setting up a call in a telecommunications network, between a user equipment operating in circuit switched mode and a destination, the method comprising the steps of: - receiving at a call routing server (102) a first circuit switched call set up request comprising a Uniform Resource Identifier, URI, as a destination identifier of the call to be set up, generating by the call routing server (102) responsive to the circuit switched call set up request a second call set up request, said second call set up request comprising the URI,

- sending (122) by the call routing server (102) the second call set up request to a translation means (103), determining (130) by the translation means (103) a telephone number corresponding to the URI of the destination. - sending the determined telephone number to the call routing server, proceeding by the call routing server with the call set up based on the telephone number.

3. The method according to claim 2, wherein the translation means (103) translates (130) the URI of the second call set up request to a corresponding telephone number of the destination.

4. The method according to any of the preceding claims, wherein said URI is a Session Initiation Protocol, SIP, URI.

5. The method according to any of the preceding claims, wherein a circuit switched call set up request is processed by the call routing server as a mobile originating call set up.

6. The method according to any of the preceding claims, wherein the URI is represented by address digits of a binary coded decimal number to identify the destination.

7. The method according to any of the preceding claims, wherein the user equipment (101 ) receives the URI in a Short Message Service message or in a Multimedia Messaging System message.

8. The method according to any of the preceding claims, wherein the user equipment (101) retrieves the URI identifying the destination, from an address book comprised in the user equipment (101 ).

9. A user equipment (101 ) for operating in circuit switched mode, adapted to request a call set up to a destination in a telecommunications network, characterized in that the user equipment comprises: an input interface (1011 ), comprising means for receiving a Uniform Resource Identifier, URI, identifying a destination of a call, a processor unit (1012), comprising means for composing a circuit switched call set up request, wherein the URI is included in the call set up request, - an output interface (1013), comprising means for sending the circuit switched call set up request, comprising the URI as the destination identifier, to a call routing server (102).

10. A user equipment (101) according to claim 9, wherein said input interface (1011 ) comprises means for receiving said URI in a Short Message Service message or in a Multimedia Messaging System message.

11. A user equipment (101 ) according to claim 9 or 10, further comprising a memory connected to the processor unit (1012) for storing one or more URIs in an address book, wherein the user equipment (101) comprises means for retrieving the URI identifying the destination from the address book.

12. A call routing server (102) in a telecommunications network comprising an input interface (1021 ), comprising means for receiving a first circuit switched call set up request, the first circuit switched call set up request requesting a call set up to a destination,

- a processor unit (1022) connected to the input interface (1021 ), comprising means for generating responsive to the first circuit switched call set up request, a second circuit switched call set up request, - an output interface (1023) connected to the processor unit (1022), comprising means for sending the second call set up request towards the destination, characterized in that the processor unit (1022) comprises means for generating the second circuit switched call set up request by processing a URI identifying the destination, said URI being comprised in the first call set up request.

13. The call routing server (102) according to claim 12, comprising means for sending a request for a destination identifier, comprising said URI, to a translation means.

14. The call routing server (102) according to claim 12 or 13, comprising means for determining if the second call set up request is to be sent towards the destination in a circuit switched mode or in a packet switched mode.

15. The call routing server (102) according to any of the claims 12-14, comprising a Mobile Switching Center.

16. A translation means (103) in a telecommunications network comprising an input interface (1031 ) comprising means for receiving from a call routing server, a request for a destination identifier, wherein the request comprises a URI,

- a processor unit (1032) connected to the input interface (1031 ), comprising means for translating the URI into the destination identifier,

- an output interface (1033) connected to the processor unit (1032), comprising means for sending the destination identifier to the call routing server.

17. The translation means according to claim 16, comprising means for translating the URI to a corresponding E.164 telephone number for identifying said destination.

18. The translation means according to claim 16, comprising means for sending the URI as destination identifier for identifying said destination in a packet switched part of the network.

19. The translation means according to any of the claims 16-18, wherein the translation means is comprised in the call routing server (102) or co-located with the call routing server (102).

20. The translation means according to any of the claims 16-18, wherein the translation means comprises a Service Control Point.

21. The translation means according to any of the claims 16-20, comprising means for processing a Binary Coded Decimal, BCD number comprised in the circuit switched call set up request, said BCD number comprising the URI.

22. A computer program product loadable into the internal memory of a digital computer, comprising software code portions for performing the steps of claim 1- 8 when said product is run on a computer.

23. The computer program product according to claim 22, stored on a computer usable medium.

24. A circuit switched call set up request message (109), characterized in that the circuit switched call set up request message comprises a Uniform Resource Identifier, URI (1091 ) as a destination identifier identifying a destination of a call set up requested by the circuit switched call set up request message.

25. The circuit switched call set up request message according to claim 24, comprising only the URI (1091 ) as destination identifier identifying the destination of the call set up requested by the circuit switched call set up request message.